1. Field of the Invention
This invention relates to receiving sheets used for dye transfer type thermal printing using a printing means, for example, a thermal head, an optical head for laser beam, et., or a head consisting of an array of electrodes. And it relates particularly to receiving sheets useful for high-speed printing and/or relative-speeds printing in which printing is conducted while controlling the relative speeds of a transfer sheet and a receiving sheet so as to make them different from each other.
2. Description of the Prior Art
It has been proposed that a polymer layer is provided between a substrate and a dyeable layer so as to improve reproducibility of dots (for instance, Japanese patent Application Kokai (laid opeon to public inspection) Nos. 61-121993, and 61-144394)). Further, it has been proposed that a removable layer which is excellent in dye permeability is additionally arranged on a dyeable thermoplastic polymer layer which is laminated on a cellulose layer in order to prevent the adhesion of a color sheet onto the polymer layer (Jap. Pat. Appln. Kokai No. 59-165688). There have been proposed various kinds of thermocurable resin as a dyeable material.
In case that a dyeable layer of a dye-receiving sheet to be used in a high-speed printing, especially a high speed relative-speeds printing system is constituted with a thermoplastic resin, a shear stress is applied on the intersurface between a coloring layer of a transfer sheet and a dyeable layer of a receiving sheet under pressure, so that the dyeable layer made of the thermoplastic resin is liable to soften up with heat on its inter-surface and to become deformed, even if a lubricant exists on the surface. Accordingly, a thermocurable resin excellent in heat resistance is useful as a material for the dyeable layer. Particularly, a moisture-curable resin in the thermocurable resins is most suitable in the aspect of an image stability because it leaves little unreacted resin on the surface of the dyeable layer. A moisture-curable resin, however, has a defect of lower curing speed in comparison with an ultraviolet curable resin which has the highest curing speed of a thermocurable resin.
As another proposal there is suggested a multi-layer dye-receiving sheet which has two or more layers on a substrate. One example of such a multi-layer dye-receiving sheet has an outer surface layer made of epoxy resin, but the curing rate is not only slower but also longer time is necessary to make the surface tack-free.
Furthermore, it includes many problems in the aspect of the image stability and recording sensitivity to provide a layer of a removable material as an upper surface layer as described in Jap. Pat. Appln. Kokai No. 59-165688, though the layer is made of a material excellent in dye permeability, because the dye from a color sheet has a tendency to be dyed predominantly on the upper surface portion of the receiving sheet.
In case of multi-layer constitution other problems will be given rise to due to the more complicated constitution than one layer constitution, for instance, increase of the cost, lowering of the producibility, and curing inhibition by oxygen, water and the like in the air, which will occur more frequently when a thinner UV-curable resin or an thinner ion-curable resin is used as combined with a thin upper surface layer made of thermocurable resin.